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Biochem Biophys Res Commun. 2009 Jul 31;385(3):291-5. doi: 10.1016/j.bbrc.2009.04.155. Epub 2009 May 6.

Pattern of rise in subplasma membrane Ca2+ concentration determines type of fusing insulin granules in pancreatic beta cells.

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Department of Biochemistry, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka, Tokyo 181-8611, Japan.


We simultaneously analyzed insulin granule fusion with insulin fused to green fluorescent protein and the subplasma membrane Ca2+ concentration ([Ca2+](PM)) with the Ca2+ indicator Fura Red in rat beta cells by dual-color total internal reflection fluorescence microscopy. We found that rapid and marked elevation in [Ca2+](PM) caused insulin granule fusion mostly from previously docked granules during the high KCl-evoked release and high glucose-evoked first phase release. In contrast, the slow and sustained elevation in [Ca2+](PM) induced fusion from newcomers translocated from the internal pool during the low KCl-evoked release and glucose-evoked second phase release. These data suggest that the pattern of the [Ca2+](PM) rise directly determines the types of fusing granules.

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